The present invention relates in general to wireless communication systems and, more particularly, to systems and methods for improving signal quality by providing select signals to a wireless communication system.
As originally implemented, cellular communications systems were broken down into omni-trunks where each cell was able to use each channel in a 360xc2x0 radius. Because of overlap in the area serviced by cells, a caller utilizing one cell in the penumbra between two cells could interfere with a caller utilizing the other cell if both were on the same channel. To avoid this interference the channel utilized by a caller in one cell would have to be disabled for any other callers in any adjacent cells. Disabling such a channel on all adjacent cells would cause many more cells than actually utilized to have the caller""s channel unavailable for use by other callers. Such disabling of channels to avoid interference was recognized to lead to under-utilization of cell resources as well as depletion of available channels.
One solution to reduce the interference problems caused by other users in the omni-trunk 360xc2x0 configuration, has been to break down cells into 120xc2x0 sectors such that each channel available at the cell only communicates in an area of 120xc2x0 radial coverage about the cell. Through the use of such sectors, mobile units operating within an adjacent cell or the same cell, but within a different sector, may utilize a different communication channel and, therefore, substantially avoid interfering with other callers in the cell.
A problem with going from the omni-trunk 360xc2x0 configuration to the sector system, however, is that as a result of splitting of the cell into 120xc2x0 sectors only a third of the channels are available in each sector. This results in a reduced call capacity in any particular cell sector as compared to that available in the omni-trunk 360xc2x0 configuration.
In order to maintain call capacity throughout the cell, other solutions to these interference problems have included the use of so called xe2x80x9csmart antennas,xe2x80x9d or switchbeam systems, providing multiple antenna beams throughout the cells. Systems implementing multiple antenna beams, such as twelve narrow beams, are described in U.S. Pat. No. 5,563,610, entitled xe2x80x9cNARROW BEAM ANTENNA SYSTEM WITH ANGULAR DIVERSITY,xe2x80x9d incorporated herein by reference, and the associated above-referenced co-pending and commonly assigned continuation-in-part U.S. Patent application entitled xe2x80x9cAPPARATUS, SYSTEMS AND METHODS FOR MULTIPLE ANTENNA TRANSMISSION IN WIRELESS COMMUNICATIONS SYSTEMS.xe2x80x9d
In such systems, a controller is operable to determine a narrow beam upon which a mobile is operating and couple that beam""s signal to the proper communication input at the base transceiver station (BTS). Therefore, the smart antenna system is able to target particular mobile units to the exclusion of others and, as a result, reduce interference caused by the mobile units not targeted. However, the ability to mitigate interference in such systems as they exist today is limited by the fact that selection of a beam for a certain channel not only provides that channel to the BTS radio, but all channels on that beam are also sent down to the BTS radio. This problem is compounded in digital systems where the same channel may be utilized on multiple beams and, thus, have increased opportunity for interfering signals to appear within the selected beams. Therefore, the amount of interference rejection that is obtained, in either an analogue or digital implementation, is not as great as could be if only the channel that was desired was sent to the radio.
Moreover, although typically providing improved signal quality over the 360xc2x0 omni-trunk configuration, both the sectored and smart antenna systems have their drawbacks to implementation. For example, since its introduction for use by the general public in the early 1980""s, mobile communications utilizing cellular telephone technology has experienced phenomenal growth. This growth has resulted in a vast base of existing BTS sites already installed and equipped throughout many cellular service areas. These BTS sites may be equipped with any number of different technologies, such as the omni-trunk, sectored cell, or smart antenna, discussed above.
In order to improve signal quality at existing BTS sites, installed without the benefit of recent communication technology improvements, it would be advantageous to provide a reduction in interference, such as through the use of the solutions above. However, the above mentioned solutions require extensive modification to existing BTS sites in order to be implemented. For example the three sectored system typically requires the addition of radio units to individually process the signals associated with the three sectors in addition to replacing the existing antenna structure. Similarly, the smart antenna typically requires modifications at the BTS site, such as usurping the operation of existing equipment, in addition to replacing the existing antenna structure in order to function properly.
The necessity to add communication equipment to provide additional functionality or in order to usurp existing functionality causes there to be a cost barrier with respect to equipping existing BTS sites with such improved technology. Moreover, as there are a plethora of different manufacturers and configurations of existing equipment, the upgrade equipment must typically be specially configured or adapted in order to upgrade a particular BTS site configuration.
Therefore, a need exists in the art for an air interface system and method which is adaptable to existing wireless communication hardware in order to provide improved signal quality at existing BTS sites.
A further need exists in the art for an air interface system and method which is universally adaptable to a variety of existing wireless communication hardware such that its installation on different configurations of systems requires little or no modification.
A still further need exists in the art for an air interface system and method which, when coupled with existing wireless communication equipment, provides improved signal quality while replacing or usurping a minimum of existing hardware.
These and other objects, needs and desires are obtained in a system and method utilizing an air interface controller to provide select signals appearing within the radiation pattern of cell to communication equipment associated with an existing BTS site. Through the provision of only select signals to the inputs of the BTS communication equipment, the present invention is capable of targeting particular mobile units to the exclusion of other mobile units. This provides for improved signal quality as the number of potential interfering signals is reduced.
Preferably, the air interface controller of the present invention provides the select signals to the exclusion of others through the use of adjustable filters. As the air interface controller determines which signals are to be provided to the communication equipment, a filter in the signal path is adjusted or selected to allow the associated frequency band, or channel, to pass.
Preferably, the air interface controller monitors the BTS in order to determine which signals are to be provided to the BTS. For example, the air interface controller may intercept BTS scan receiver commands in order to determine what communication channels to pass, through the use of the above mentioned filtering, to the BTS. It shall be appreciated that, by utilizing information already available at the BTS in order to make its determination of what signals to pass, the present invention does not require duplication or usurpation of the existing BTS control systems. Furthermore, by simply requiring connection to already existing, commonly available, control signals, rather than usurping various control systems, the present invention does not require significant modification to couple with a variety of existing BTS sites. Therefore, the present invention is a true applique that may simply be added to a previously existing BTS in order to improve signal quality.
Furthermore, the air interface controller of the present invention includes a minimum amount of hardware, and is thus cost effective to implement. This, combined with the fact that the air interface controller is an applique, results in an apparatus uniquely suited for retrofitting BTS sites already in place. Therefore, a technical advantage of the present invention is to provide a convenient means by which signal quality may be improved at existing BTS sites through the addition of an upgrade applique to existing hardware.
It shall be appreciated that the use of the signal filtering described above is advantageous in reducing interference, even at an omni-trunk cell, as only signals of interest are allowed to pass to the BTS. However, by definition, each of the communication channels associated with these signals of interest are communicated throughout the omni-trunk cell.
Therefore, to provide the additional benefits associated with antenna beams targeting select mobile units to the exclusion of others, a preferred embodiment of the present invention utilizes multiple narrow beams. An aerial structure adapted to provide multiple narrow beams and their associated signals is described in the above-referenced co-pending and commonly assigned U.S. patent application entitled xe2x80x9cCONICAL OMNI-DIRECTIONAL COVERAGE MULTIPLE-BEAM ANTENNA WITH MULTIPLE FEED NETWORK.xe2x80x9d Of course, either adaptive arrays or fixed multi-beam arrays could be utilized by the present invention.
This embodiment of the present invention determines which signals should be passed to the BTS, and then determines the beams having the most desirable signal (i.e., strongest received signal, best signal to noise ratio, highest carrier to interference ratio, etc.) with respect to the signal of interest. Upon making this determination, the air interface controller adjusts a filter in the signal path associated with these select beams to allow the frequency band associated with the signal of interest to pass. As such, the air interface controller filters signals appearing within the antenna beam, on a per beam basis, such that only the channels that should be allowed to travel to the radio for a specific beam are allowed to do so.
The purpose of the air interface controller selecting from among beams upon which the signal of interest appears is to provide the BTS with the signals of interest with the best signal possible. This removes the excess interference that is caused by a signal, which may be present on an adjacent beam but is not strong enough to be helpful to the desired signal on the first beam, which may cause interference to a second channel on the adjacent beam.
For example, the present invention may select the two beams having the strongest signal with respect to a signal of interest. The filters provided in the signal paths of these two beams may then be adjusted to pass the communication channel associated with this signal of interest. All the remaining beams would be essentially shut off with respect to this signal of interest. This way, not only are mobile units operating outside these two beams excluded, but so to are mobile units operating on different communication channels within these beams. Likewise, this signal is removed from other beams which may be utilized to service other communication units.
It shall be appreciated that, although a sectored or typical smart antenna system may select a beam or sector having a best attribute with respect to a signal of interest, generally these systems pass all signals present within the beam signal to the BTS communication equipment. There are typically signals in addition to the signal of interest appearing within the antenna beam signal which, when allowed to pass to the communication equipment, may cause interference with the signal of interest. Such interference may be in the form of cross channel or co-channel interference or may be in the form of reducing the signal to noise ratio or carrier to interference ratio.
As with the previously described embodiment, this embodiment preferably monitors the BTS in order to determine which signals are to be provided to the BTS. Utilization of such information already available at the BTS, in order to make its determination of what signals to pass, does not require duplication or usurpation of the existing BTS control systems. Such connection to already existing, commonly available, control signals, also does not require substantial modification to couple with a variety of existing BTS sites. Therefore, this embodiment of the present invention is an appliquxc3xa9 that may simply be added to a previously existing BTS in order to improve signal quality.
As such, the multiple beams of the present invention are essentially compressed down to 2 beams and interfaced into the cell site BTS. Therefore, instead of having a switch matrix of any sort, the interference rejection is accomplished through the filtering of each of the multiple antenna beams which are then summed together and allowed to pass to the cell site. Using this method, the application is completely transparent to the cell site. This provides equipment that, although not specifically manufactured for a particular BTS configuration, any cell site containing two inputs for an omni or six inputs for a sector can easily utilize to obtain greater capacity and interference reduction.
However, it shall be appreciated that in order to provide multiple narrow beams at a cell previously having only an omni-trunk, or even a typical sectored, configuration, this embodiment replaces the existing aerial structure. Therefore, although being an appliquxc3xa9 coupled to the BTS, this embodiment does not interface between existing antenna structure and communication equipment as the previously described embodiment, but rather attaches to the BTS and replaces the existing aerial structure. Of course, where a multi-beam aerial structure exists, the present invention may utilize such without the need to replace the structure.
A technical advantage is realized by the present invention in its ability to improve the signal quality at any type of BTS. Specifically, by providing only signals of interest to the BTS communication equipment through the use of filters, the present invention is able to improve signal quality. This signal improvement may be further enhanced through the use of interference cancellation accomplished by removing interfering signals from the signal of interest. Moreover, through the use of multiple beam antenna structure, the present invention is further able to improve signal quality through selection of beams providing the most desirable signals of interest.
A further technical advantage of the present invention is improved signal quality over a typical multi-beam antenna system as the adjustable filters are utilized to select only the signals of interest on the antenna beam signals passed to the BTS communication equipment to the exclusion of other signals appearing therein. As such not only are mobile units operating outside a particular antenna beam excluded, but so to are mobile units operating on other channels within the beam.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and the specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims.